Supporting Information

Transcription

1 1 Supporting Information 2 3 Deep Oxidation of NO by a Hybrid System of Plasma N-type Semiconductors: High-Energy Electron-Activated Pseudo Photocatalysis Behavior 4 5 Si Chen 1,2, Haiqiang Wang 1,2*, Mengpa Shi 1,2, Haoling Ye 1,2, Zhongbiao Wu 1, Key Laboratory of Environment Remediation and Ecological Health, Ministry of Education, 8 College of Environmental & Resources Science, Zhejiang University, Hangzhou , P.R. 9 China; Zhejiang Provincial Engineering Research Center of Industrial Boiler & Furnace Flue Gas 11 Pollution Control, Hangzhou , P.R. China; * Corresponding author: 15 (H. Wang) haiqiangwang@zju.edu.cn ; Tel. / Fax: Full postal address: Key Laboratory of Environment Remediation and Ecological Health, Ministry 17 of Education, College of Environmental & Resources Science, Zhejiang University, Hangzhou , P.R. China Number of pages: 16 Number of Tables: 3 22 Number of Figures: 10 1

2 23 2

3 24 Text S The DBD reactor design. Stainless steel wire tightly twined around a quartz tube with inner diameter of 20 mm and thickness of 5 mm was used as high-voltage electrode. A ceramic tube filled with metal powder was located in the axis of the quartz tube with an outer diameter of 13 mm, while the ground electrode was metal powder. A dual dielectric coaxial DBD reactor was established with 200 mm long discharge region. Two axial radiator fans of adjustable power were installed on both sides of the reactor, to maintain it at room temperature as much as possible (Figure S2), the reaction rate constant through reaction process was assumed as invariant. Catalysts (2-3 g) coated on glass balls (36 g) were packed in the discharge zone. A modulating pulse power up to 500 W in the frequency range of 5 20 KHz, along with a duty cycle of 1 99% was provided by Nanjing Suman Plasma Technology Co. The analysis system. A Bruker ALPHA-G spectrometer (Bruker, Germany) with 0.5 L gas cell was the primary analytical method in this study and a spectrum was obtained by overlapping 16 scans at the resolution of 4 cm -1. This infrared analysis system was applied to evaluate the types of gaseous products and to determine the concentration of NO/NO 2 /N 2 O. O 3 was measured by O 3 analyzer (UV-100, Eco Sensors in America). The assessment of energy consumption. To assess energy consumption, a digital oscilloscope (TDS2014C, Tektronix), high-voltage probe (P6015A, Tektronix), and current probe (CP8030B, Zhiyong) were introduced to measure the waveform, voltage, and current, respectively. The duty ratio and the modulation frequency of the 3

4 modulating pulse power were fixed at 60% and 64 HZ for all tests, respectively. Detailed information about the discharge characteristics and the correlation between applied voltage and SIE were shown in Figure S3 and Table S1, respectively. 49 Text S Catalysts selection. In consideration of the band gap energy and the ability of generation of O 2 - and OH, six kind of typical N-type catalysts were chosen for tests as follows: ZnO (E CB =-0.31ev, E VB =2.92ev, Eg=3.32ev, can produce OH), P25 53 (E CB =-0.8ev, E VB =2.4ev, Eg=3.2ev, can produce both O 2 - and OH), WO 3 54 (E CB =0.64ev, E VB =3.44ev, Eg=2.8ev, can produce OH), In 2 O 3 (E CB =-0.52ev, 55 E VB =2.08ev, Eg=2.6ev, can produce both O 2 - and OH), CdS (E CB =-0.52ev, E VB =1.88ev, Eg=2.4ev, can produce O 2 - ) and Fe 3 O 4 (E CB =1.23ev, E VB =1.33ev, Eg=0.1ev, can t produce O 2 - and OH). 58 Text S Characterization. The specific surface areas were determined with a static adsorption instrument (JW-BK 132F, Beijing JWGB Sci & Tech Co., China) by the Brunauer-Emmett-Teller (BET) method. The NO-TPD was carried out on TP-5079, samples were saturated with NO (6% in He) for 30 min at 30 o C prior to heating the sample in He from 30 to 300 o C with a heating rate of 10 o C/min. The temperature of the DBD reactor was measured by AR300 Infrared Thermometer. 65 Text S4 66 Transmission infrared analysis. Further, the fresh and used catalysts (taking CdS as 4

5 typical case) were characterized by transmission infrared spectrometer, as exhibited in Fig. 7a. For fresh CdS, the broad band centered at 3410 cm -1 and the band at 1630 cm -1 were contributed to the surface adsorption of water molecules 1. The bands at 1387, 1152, 1012 and 616 cm -1 can be attributed to the Cd-S bond 2. In the case of used CdS, the intensity of peaks (3410 and 1630 cm -1 ) for the surface adsorption of water molecules weakened, indicating the consumption of the surface adsorbed water molecules during the reaction process, along with the strong peaks (1395 and 1348 cm -1 - ) for surface absorbed NO 3 3 and peaks (1109 and 1071 cm -1 ) for liner nitrite 4 being observed. Besides, the weak bands at 1768 and 830cm -1 were attributed to the coordination of a monodentate nitrate ion, Cd-NO 5-3 and NO 6 3, respectively. The IR bands in the region of cm -1 were assigned to Cd-H 2 O 5. Evidently, results from transmission infrared spectra revealed the formation of NO - 2 and NO

6 80 List of Tables Table S1. The correlation between applied voltage and the specific input energy (SIE). Table S2. Some reactions related to the process. Table S3. The surface areas of Co 3 O 4, P25, CdS and Fe 3 O

7 86 Table S1. The correlation between applied voltage and the specific input energy (SIE). Voltage regulator (V) Input peak voltage (KV) SIE (J/L) Table S2. Some reactions related to the process Reaction Reaction A a E a n Order Refs ID (kj mol -1 ) R1 O + N NO 6.89E (7) R2 O 2 + N 3 N 2 O + NO (8) R3 N 3 + O N 2 + NO 1.12E (9) R4 O 2 + N NO + O 1.50E (10) R5 N( 2 D) + O 2 NO + O 1.22E (11) R6 NO 2 + O NO + O 2 5.5E (12) R7 NO + O + M NO 2 + M 2.99E (13) 88 a: units First orders: s -1, Second order: cm 3 /(mole s), Third order: cm 3 /(mol 2 s) 89 Table S3. The surface areas of Co 3 O 4, P25, CdS and Fe 3 O 4 Catalyst Co 3 O 4 P25 Fe 3 O 4 CdS A BET (m 2 /g)

8 90 List of Figures Figure S1. Overall principal diagram for the experimental system. Figure S2. The variation temperatures of the DBD reactor during reaction process. Figure S3. The discharge characteristic of DBD: (a) the waveform of modulating pulse consist of multiple square-wave; (b) the waveform of voltage and current of one square-wave; (c) the expanded view of one square-wave; (d) the waveform of voltage and current of one sine wave; (e) the waveform of power and energy of one sine wave; (f) the waveform of power and energy of one square-wave. Figure S4. IR spectra of NO removal with SIE by plasma cooperating with P-type materials (a) Co 3 O 4, (b) BiOI and (c) Ag 3 PO 4. Figure S5. IR spectra of plasma cooperating with Fe 3 O 4 with excess addition of (a) hole trapping agent Na 2 C 2 O 4, and (b) electron trapping agent K 2 Cr 2 O 7 ; and P25 with excess addition of (c) hole trapping agent Na 2 C 2 O 4, and (d) electron trapping agent K 2 Cr 2 O 7. Figure S6. IR spectra of NO removal with SIE by plasma cooperating with sole trapping agents (a) Na 2 C 2 O 4 and (b) K 2 Cr 2 O 7. Figure S7. Comparison of discharging in P25/glass ball with the addition of 100 ppm water vapor or not: (a) the quantitative analysis and (b) the IR spectra. Figure S8. NO-TPD of Co 3 O 4, P25, CdS and Fe 3 O 4. Figure S9. IR spectra of glass balls impregnated with NO and NO 3 discharging in N 2 + 6% O 2. Figure S10. The cycle activity test: (a) and (b), the longtime test at 214J/L: (C) and 8

9 112 (d)

10 Figure S1. Overall principal diagram for the experimental system Figure S2. The variation temperatures of the DBD reactor during reaction process

11 Figure S3. The discharge characteristic of DBD: (a) the waveform of modulating pulse 122 consist of multiple square-wave; (b) the waveform of voltage and current of one square-wave; (c) 123 the expanded view of one square-wave; (d) the waveform of voltage and current of one sine wave; 124 (e) the waveform of power and energy of one sine wave; (f) the waveform of power and energy of 125 one square-wave. 11

12 Figure S4. IR spectra of NO removal with SIE by plasma cooperating with P-type materials (a) 128 Co 3 O 4, (b) BiOI and (c) Ag 3 PO

13 Figure S5. IR spectra of plasma cooperating with Fe 3 O 4 with excess addition of (a) hole trapping 132 agent Na 2 C 2 O 4, and (b) electron trapping agent K 2 Cr 2 O 7 ; and P25 with excess addition of (c) hole 133 trapping agent Na 2 C 2 O 4, and (d) electron trapping agent K 2 Cr 2 O Figure S6. IR spectra of NO removal with SIE by plasma cooperating with sole trapping agents (a) Na 2 C 2 O 4 and (b) K 2 Cr 2 O 7. To analyze the influence of trapping agents, comparison experiments of sole trapping agents-catalyzed discharging process of NO degradation under same condition were done (Fig. S6). Nearly identical consequence were obtained compared with the blank sample, which indicated that the addition of trapping agents may almost do not affect the plasma process and the experimental results. 13

14 Figure S7. Comparison of discharging in P25/glass ball with the addition of 100 ppm water vapor 144 or not: (a) the quantitative analysis and (b) the IR spectra Figure S8. NO-TPD of Co 3 O 4, P25, CdS and Fe 3 O 4. As shown in Table S3 and Figure S8, four kinds of semiconductor catalysts (Co 3 O 4, P25, CdS and Fe 3 O 4 ) were selected, to study the influence of catalysts surface areas and absorption capability on this process. The BET results showed CdS owned the largest surface areas while Co 3 O 4 the minimum, P25 and Fe 3 O 4 were intermediate. As for NO-TPD with MS NO signal, CdS illustrated the most distinct peak of NO desorption at 261 o C, Co 3 O 4 followed at 251 o C, showing better absorption 14

15 capability of NO. While both of the NO desorption peaks for P25 and Fe 3 O 4 were very weak but at lower temperature, indicating that the absorbed NO by P25 and Fe 3 O 4 could be activated more easily. Integrating results of Table S3, Fig. S8 and the previous activity tests, it was acceptable that the larger surface areas and better absorption capability would activate more reactants, but may not tip the scales Figure S9. IR spectra of glass balls impregnated with NO 2 - and NO 3 - discharging in N 2 + 6% 160 O To verify the stability of NO 2 - and NO 3 - during the plasma process, suitable amount of NO - 2 and NO - 3 were impregnated on the glass balls by equivalent-volume impregnation in mixed solution of ppm NO - 2 and ppm NO - 3, prior to discharging in N 2 +6% O 2, as shown in Figure S9. There was no new peaks for NO x compared with the blank, illustrating the nitrates on the surface of catalysts were stable during the discharging process. 15

16 Figure S10. The cycle activity test: (a) and (b), the longtime test at 214J/L: (C) and (d). A cycling test and a long time experiment were carried out to investigate the stability of photocatalysts in plasma process, taking the CdS as an example. As shown in Figure S10, CdS can maintain activity within five circles or about 400 min at 214J/L, and the inactivation of CdS would gradually came into being due to the deposition of nitrates. After the treatment of water washing for the used catalysts, it can work again. Hence, it is verified that the plasma-semiconductor catalysts hybrid system is promising and meaningful. On the other hand, available ways for further enhancement of the stability of photocatalysts in plasma process need to be paid more attention in the future study

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